Lab 5 -- Animal Behavior
Behavior encompasses a diverse set of activities, from simple responses to external stimuli (e.g., the knee-jerk reflex in humans) to complex communication and social interactions (e.g., the social behavior of whales, birds, or ants). Although one could argue persuasively that all organisms "behave" in some way, the term is customarily used to describe the activities of animals, individually or in groups. The study of animal behavior (ethology) was founded by Niko Tinbergen, Konrad Lorenz, and Karl von Frisch, all of whom used an evolutionary outlook to ask how and why animals behave as they do.
Questions about animal behavior fall into four categories, defined by whether they concern proximate issues ("How" questions) or ultimate ones ("Why" questions), and by whether they consider the causes or the origins of behavior. To approach a complete understanding of animal behavior requires asking all four kinds of questions.
Kinds of questions about animal behavior
How? Proximate mechanism (physiology) development, genetics
Why? Ultimate adaptiveness phylogeny
Proximate questions are usually posed at the level of individual organisms. Questions about proximate causes often concern individual physiology (e.g., How and with what sensory modes does a bird perceive that it is time to breed? How does that perception stimulate mating behavior by affecting the endocrine or nervous systems?). Proximate questions about the origins of behavior deal with individual development (e.g., How does a juvenile bird's sensory apparatus develop? How does a juvenile develop courtship behavior?) or genetics (e.g., How is the timing of breeding behavior inherited?). Ultimate questions, which concern evolutionary reasons for behavior, are posed at the population level or above. These may concern evolutionary causes (Why does breeding time matter to survival and reproductive success in this bird population's environment?) or origins (What is the contribution of evolutionary ancestry to this species' breeding time?) The contemporary field of behavioral ecology focuses primarily on ultimate questions, but uses information about proximate causes and origins to formulate those questions.
In this lab exercise, you will develop skill at addressing questions about animal behavior through the study of an important kind of decision all animals make at some time in their lives: choosing where to position themselves in space (habitat choice). The details of these kinds of decisions will vary among kinds of animals, but in all cases there are potential fitness consequences of the choices individuals make. For example, an organism's choice of habitat may affect its food supply, its exposure to sources of stress and mortality (e.g., competitors, predators), and its probability of finding suitable mates. You should think of habitat choice in a very broad sense, including choosing among different types of physical environments, choosing whether to live alone or in a group, choosing among types of food, and choosing where to rear offspring.
Since animal behaviors can be very complex and may require a great deal of familiarity with the experimental animals, a lab only two weeks long must concern behaviors that are relatively easy to observe and quantify. Each station located in the lab has handouts describing a simple behavior (a kind of habitat choice in the broad sense) of one of several kinds of animals. Each handout describes a simple experiment or set of observations you can perform to test a behavioral hypothesis. This week, you should find your group's assigned station and carry out the simple experiment suggested. Analyze the results as directed to find out whether the stated hypothesis is supported.
Based on your findings and your intuitions about the behavior in question, you should then devise your own experiment that extends your understanding of the behavior. The experiment should address a specific hypothesis, and you should consider the important features of experimental design, i.e., independent and dependent variables, proper controls, replication, etc. You should design your experiment with a statistical test in mind for determining the significance of your results.
Let your instructor know if you require any additional materials to perform your experiment. We reserve the right to deny permission for any experiment that we consider inappropriate. Run your ideas for an experiment through one of the TAs or Mrs. Kolbe first. If it needs revision, do so before asking for approval from your instructor. After receiving approval for your design, fill out the proposal form and hand it in to Mrs. Kolbe.
Before your next lab period, you should do some literature research on your organism. Knowing about an organism's natural environment, including its resources and predators can be critical to understanding aspects of its behavior. Also, understanding the sensory modes of animals is crucial to the design of your experiment. Remember that many organisms do not sense stimuli as we do (e.g., bats use echolocation, bees see UV light, amphibians can only detect moving stimuli, etc.).
Perform your experiment.
As a group, present your findings orally to the class.
Format for oral presentations
At scientific meetings, spoken presentations usually take one of three forms: (1) addresses or "full-length" research talks, usually 45-50 minutes long, plus about 10 minutes for questions; (2) symposium talks, which are 20-30 minutes long, including a question period; or (3) "contributed papers", usually consisting of a 10-15 minute talk with 2-5 minutes left for questions.
To present the results of your animal behavior projects, you need to prepare a "contributed paper" talk of about 12 minutes, including 2 minutes for questions. Each group of students should hand in a title for their project to Mrs. Kolbe at least 24 hours before the scheduled lab. We will determine the order of presentations by a random process. Since there will be two or three of you presenting each project, you need to decide how to share the work (e.g., if three are presenting, one could present the introduction, one the m&m and results sections, and the third could present the discussion).
Sections of your talk
Introduction (~3 minutes). Give the audience the scientific context for your project. Tell us why we ought to be interested in hearing about it. Tell us briefly what you did (i.e., tell us what you're going to tell us). Tell us your expectations and specific hypotheses, if any. Give us a hint about your major findings. Use visual aids (chalkboard, overhead projector transparencies*) if you think that will help. By the end of this section, we should know exactly what phenomenon you investigated and what questions you asked about it.
Methods and materials (~ 2 minutes). Tell us where and when you did the work (in general and in particular). Explain why you chose to collect the data that you collected, and how those data allow you to answer your question(s). Tell us about your statistical methods, and justify them if necessary. Again, use visual aids if you think they will help convey your message. By the end of this section, we should understand what you did well enough to explain it to someone else.
Results (~ 2-3 minutes). Tell us what you found. What do your data say about your questions? Strive to be clear. Visual aids of some kind are certainly appropriate in this section. Make sure they are as clear as possible, so that they get your main points across.
Discussion (~ 2-3 minutes). Make this short and sweet, but don't rush. Repeat the major findings of your study and the major conclusion (in terms of your initial question[s] and/or hypotheses). This is what you want us to remember most about your project. Discuss a few of your work's implications. Were there any surprising results? What would be an interesting follow-up project? What new questions did your study generate?
Question period (~2 minutes). All group members together accept questions from the class. Give brief, thoughtful, respectful answers. Have the questioner repeat the question if you don't understand it at first.
* Procedure for preparing overhead transparencies
If you would like to make photocopied overhead transparencies for your presentations, you may arrange this through your instructor. Prepare your figures and/or text at least 24 h before you need them (48 h would be better). Deposit these in the "drop box" outside your instructor's door. Your instructor will have the Science Division secretaries make high-quality transparencies. You may pick these up (along with your originals) from the "pick-up" box one day later. If you need any "last minute" transparencies (were not recommending this, however), you must buy blank transparencies at the bookstore and make them yourself.
Drosophila melanogaster -- Taxis
Taxis (pronounced like "taxes" not "tax-ease") refers to directed reactions of animals either toward or away from a stimulus (positive taxis and negative taxis, respectively), where the long axis of the body is oriented toward the source. For example, the flight of moths toward light is positive phototaxis. Animals can react to chemicals (chemotaxis), gravity (geotaxis), heat (thermotaxis), etc.
Drosophila are a diverse genus of flies that use all manner of rotting food sources of non-animal origin. When organisms' survival and reproduction depends on finding such patchy, ephemeral resources, selection favors the ability to find new habitats from long distances with great precision.
In this exercise you will characterize some tactic responses of Drosophila . This week's simple experiment examines geotaxis. Your hypothesis will be that the flies exhibit geotaxis, either positive (towards gravity, i.e., down) or negative (away from gravity, i.e., up). You decide which form you expect. The null hypothesis is that the flies will exhibit no geotaxis -- no tendency to move up or down. When you design your experiment for next week, think about what kinds of responses to other stimuli might make evolutionary sense, given the lifestyle of Drosophila..
Your instructors have given you 10 flies, each enclosed in section of clear plastic tubing capped on both ends with corks. The midpoint of each tube is marked, and the ends are labeled "A" or "B". For today's experiment you will need one or more stopwatches (or wristwatches with stopwatch functions) and a test-tube rack.
For each replicate of the experiment, take a tube and place it upright in a test-tube rack, using a random procedure to assign either the "A" or "B" end to be the top. Immediately take a stopwatch and, for 2 min., record the time the fly spends in each half of the tube. (You need not keep track of the time spent in each half separately. Time spent on one side is just 2 min. [120 sec.] minus the time spent on the other. Of course, you do need to keep track of total time.) When you have completed 10 replicates, calculate the mean, standard error (SE), and 95% confidence interval (mean ± 2 x SE) for time spent on one half of the tube. If this confidence interval does not include 60 sec. (which is what you would expect for the null hypothesis), then Drosophila exhibit some kind of geotaxis.
Crayfish -- Habitat Preferences
Crayfish (Cambarus) are freshwater crustaceans that live in streams and lakes, foraging on the floor of these bodies of water. Because they occur on many kinds of underwater substrates (surfaces), they are ideal subjects for studies of habitat choice. In addition to foraging needs, a significant selective factor in crayfish habitat choice is the need for refuge from vertebrate predators (e.g., fish, humans, raccoons).
In this exercise you will examine the habitat choices of crayfish presented with alternative environments. This week's simple experiment concerns the habitat choice -- if any -- that crayfish make when presented with two contrasting substrates: fine sand and small river rocks. Your hypothesis is that individual crayfish express a preference for one kind of substrate over the other. Make a guess about which one they prefer. The null hypothesis is that crayfish exert no preference for one of these substrates. For next week, design an experiment to refine your understanding of how crayfish choose habitats.
Your instructors have given you a crayfish "arena" (washtub). Half of the arena's floor consists of fine sand, while the other half consists of river rocks. You will need a stopwatch (the one on your wristwatch would be fine, if you have one).
For each replicate of the experiment, orient the experimental arena randomly with respect to compass direction, and pick up a crayfish carefully from the stock pond (approach it from behind and lift it by its thorax with one hand; they can give you an unpleasant pinch). Set the crayfish on the midline of the experimental arena, choosing its orientation (sand to the crayfish's left or sand to the crayfish's right) by a random procedure. Give the animal 1 min. to recover from being disturbed. Then use a stopwatch to record how much of a 5 min. period the animal spends on each substrate type. (To do this, of course, you only need to record the time it spends on one substrate type, since the time spent on the second type is just 300 sec. minus the time spent on the first.) When you have completed 10 replicates, calculate the mean, standard error (SE), and 95% confidence interval (mean ± 2 x SE) for time spent on one of the substrate types. If this confidence interval does not include 150 sec. (which is what you would expect on the null hypothesis), then crayfish exhibit a preference for one of the substrate types.
Minnows -- Schooling behavior
Many organisms live in groups of conspecifics. Some fish are particularly striking in this behavior, as they travel through their environment in groups or "schools," virtually never leaving the proximity of others of the same species. The function of schooling behavior is generally presumed to be increase in safety from attack by predators. But how does an individual decide what group to join? How do groups form and remain cohesive. Your experiment will address the simple, proximate question of whether a minnow decides on the group it will join based on group size. The null hypothesis is that it will not show a bias towards joining groups of different size. Decide upon an alternative hypothesis that makes sense to you. After determining the significance of your results, design an experiment to perform next week that refines the group-size hypothesis, or tests another hypothesis.
Obtain a 5 gallon "test" tank -- it should have removable glass partitions that will allow you to divide the tank into 3 chambers. The central chamber should have a line drawn on the outer glass that visually divides the central chamber in two. Place 10 minnows in one of the outer chambers, and a single minnow in the other outer chamber. For each replicate of the experiment, place an "experimental" minnow in the central chamber. Give the animals at least 1 min. to recover from being disturbed (and try not to disturb them during the observation period). Use a stopwatch to record how much of a 5 min. period the experimental animal spends on the 10-minnow side of the central chamber. Place the experimental minnow in a holding tank and get another from the stock tank. When you have completed five replicates, switch the 10- and 1-minnow chambers to the opposite ends (Why is it important to do this?). After five more replicates, calculate the mean, standard error (SE), and 95% confidence interval (mean ± 2 x SE) for time spent on the 10-minnow side. If this confidence interval does not include 150 sec. (which is what you would expect for the null hypothesis), then minnows exhibit a bias for one of the group sizes.
Terrestrial Isopods -- Habitat preferences
Terrestrial isopods (woodlice or pillbugs) are commonly observed members of the Arthropod subphylum Crustacea. They are often found during the day in aggregated groups beneath stones, wood debris and in leaf mold in gardens, woods and (in this case) greenhouses. But what environmental features of such secluded places draw them to congregate there? Since most isopods are marine, rather than terrestrial, one possibility is that differences in humidity, or moisture content of the air, are important cues for habitat selection. Your first experiment will test the hypothesis that terrestrial isopods show a bias in habitat selection among areas that differ in humidity. You should then design an experiment that refines this hypothesis, or tests another hypothesis with respect to the nature or mechanism of habitat selection.
The experimental arenas for this test will be plastic petri dishes. Obtain two half circles of filter and wet one down with water. Place them inside the dish, making sure they do not make contact (if they do the water will wick from the wet to dry piece). Place an isopod in the center of the dish and put the top on. Give the animal 1 min. to recover from being disturbed. Then use a stopwatch to record how much of a 5 min. period the animal spends on the wet side. Return the animal to a holding container, change the filter paper, and test another animal. When you have completed 10 replicates, calculate the mean, standard error (SE), and 95% confidence interval (mean ± 2 x SE) for time spent on one of the substrate types. If this confidence interval does not include 150 sec. (which is what you would expect for the null hypothesis), then isopods exhibit a bias with respect to humidity.
Crickets -- Habitat Preferences
House crickets (Acheta domesticus) are a native European species that have been introduced into N. America. They are often found overwintering in in homes in the eastern U.S. In nature, they are found in a variety of habitats, so they are ideal subjects for studies of habitat choice. Choice of habitats with different soil types may influence the ability of crickets to locomote, find food, or find refuge from predators.
In this exercise you will examine the habitat choices of crickets presented with alternative habitats. This week's simple experiment concerns the habitat choice -- if any -- that crickets make when presented with two contrasting substrates: fine sand and soil. Your hypothesis is that individual crickets express a preference for one kind of substrate over the other. Make a guess about which one they prefer. The null hypothesis is that crickets exert no preference for one of these substrates. For next week, design an experiment to refine your understanding of how crickets choose habitats.
Your instructors have given you a cricket "arena" (circular dish). Half of the arena's floor consists of fine sand, while the other half consists of soil. You will need a stopwatch (the one on your wristwatch would be fine, if you have one).
For each replicate of the experiment, orient the experimental arena randomly with respect to compass direction, and pick up a cricket carefully from the "big house." Set the cricket on the midline of the experimental arena, choosing its orientation (sand to the crickets's left or sand to the cricket's right) by a random procedure. Give the animal 1 min. to recover from being disturbed. Then use a stopwatch to record how much of a 5 min. period the animal spends on each substrate type. (To do this, of course, you only need to record the time it spends on one substrate type, since the time spent on the second type is just 300 sec. minus the time spent on the first.) Return the cricket to a holding container (so you dont use the same one twice). When you have completed 10 replicates, calculate the mean, standard error (SE), and 95% confidence interval (mean ± 2 x SE) for time spent on one of the substrate types. If this confidence interval does not include 150 sec. (which is what you would expect on the null hypothesis), then crickets exhibit a preference for one of the substrate types.